Smoking associated with PAD in women, even decades after stopping

Smoking significantly increased the risk for symptomatic peripheral artery disease (PAD) in women in a dose-dependent manner, a new study found. Those who quit reduced their risk, but it remained elevated compared with women who never smoked.

Researchers conducted a prospective cohort study using data from 39,825 participants in the Women's Health Study with no cardiovascular disease who were followed for a median of 12.7 years and surveyed about their past and current smoking habits. Results appeared in the June 7 Annals of Internal Medicine.

Current smokers were asked the average number of cigarettes they smoked per day at study entry and were asked again annually for five years, and three more times during the observational follow-up. On the basis of their answers, women were classified as never smokers, former smokers, current smokers who smoked fewer than 15 cigarettes per day, or current smokers who smoked 15 or more cigarettes per day.

Pack-years of cigarette smoking were calculated by multiplying the midpoint of the total number of years smoked by the average number of cigarettes smoked per day on the baseline questionnaire. For women who had quit smoking before enrollment, researchers subtracted the midpoint of the age category when they reported quitting smoking from their age at enrollment.

In the study, 178 confirmed PAD events occurred, defined as intermittent claudication or lower-extremity artery revascularization. Self-reported PAD was confirmed by interview and medical records. Across the four smoking categories (never, former, <15 cigarettes/d, and ≥15 cigarettes/d), age-adjusted incidence rates of PAD were 0.12, 0.34, 0.95, and 1.63 per 1,000 person-years of follow-up, respectively. Multivariate adjustment had little effect on this relationship. Adjusted hazard ratios for PAD compared to women who had never smoked were 3.14, 8.93 and 16.95, respectively.

Lifetime exposure showed a strong dose-response relationship. In age-adjusted models, hazard ratios among women whose lifetime exposure was fewer than 10, 10 to 29, or 30 or more pack-years were 2.3, 6.43 and 11.06, respectively, compared with women who never smoked. Compared with current smokers, the adjusted hazard ratios for fewer than 10 years, 10 to 20 years, more than 20 years, or lifelong abstinence were 0.39, 0.28, 0.16 and 0.08, respectively.

“Although our data show no particular threshold below which smoking does not confer an increased risk, women who indicated at least 10 pack-years of smoking exposure had a particularly steep risk increase,” the authors wrote. They continued that while it's better not to have started smoking, the message to stop is still important. “For patients and their physicians, our findings suggest that long-term smoking cessation substantially reduces the risk for symptomatic PAD, whereas the residual risk even among former smokers who abstain for at least 20 years underscores the importance of primary efforts for smoking prevention.”